HEATS OF TRANSFER AND ACTIVATION-ENERGY FOR BOUND WATER DIFFUSION IN WOOD

Concepts of nonequilibrium thermodynamics are used to discuss two molar heats of transfer associated with diffusion of water in wood. These different heats of transfer originate from energy flows that are referenced to enthalpies of water vapor and bound water. They represent heat that must be absorbed by the vapor or sorbed water phases, respectively, to maintain constant local temperatures and pressures during the process of steady-state diffusion. In addition, equations for bound water flux and moisture conductivity are used to show that the heat of transfer for absorbed water exceeds the activation energy for bound water diffusion. The distinction between these quantities remains unclear, but may be related to diffusing molecules which carry energy in excess of the minimum required for participation in diffusion.